Embodiments of the invention relate generally to diagnostic imaging and, more particularly, to a system and method of estimating hemodynamic information.
Non-invasive imaging technologies allow images of the internal structures or features of a patient to be obtained without performing an invasive procedure on the patient. In particular, such non-invasive imaging technologies rely on various physical principles, such as the differential transmission of x-rays through the target volume, measurement of resonant magnetic signals, or the reflection of acoustic waves, to acquire data and to construct images or otherwise represent the observed internal features of the patient.
For example, Coronary Computed Tomography Angiography (CCTA) is an imaging application that has evolved with the introduction and improvement of computed tomography (CT), an imaging technology based on the observed transmission of x-rays through the patient for a range of angular positions that is sufficient for image reconstruction. With the introduction of multi-slice CT scanners (e.g., 4-slice, 16-slice, 64-slice and so forth) and faster rotation speeds (e.g., about 0.35 seconds to about 0.5 seconds for a full gantry rotation), it has become possible to generate useful images of the heart. With current high-resolution (both spatial and temporal) 64-slice scanners, image quality is sufficient for CCTA to provide clinicians an imaging technique that has high negative predictive value (ratio of true negative classifications to the total number of negative classifications). In other words, the CCTA technology is very accurate in assessing patients that do not have disease. However, false positives may still occur at undesired frequency, reducing the positive predictive value of CCTA (ratio of true positive classifications to the total number of positive classifications). As such, advances are needed to improve the clinical utility of CCTA.
Further, CCTA typically provides only anatomical information of the heart and vascular structures. It may also be useful to provide various functional assessments, such as of territorial myocardial perfusion, which would be useful in determining if a narrowing in a coronary vessel (stenosis) due to atherosclerotic plaque is affecting cardiac function. There are various methods to assess cardiac function: treadmill stress test, stress echocardiogram, myocardial stress perfusion imaging (using Single Photon Emission Computed Tomography (SPECT)), Positron Emission Tomography (PET), CT perfusion, or invasive assessment of cardiovascular hemodynamics (fractional flow reserve (FFR)).
Combining both anatomical information and a correlated per territory assessment of resulting cardiac function may be useful in the clinical evaluation of cardiac disease. One approach, percutaneous coronary intervention (PCI), may provide this capability using anatomical information via projection coronary angiography and functional information through coronary blood pressure measurements from a transducer in the coronary vasculature. However, these procedures are highly invasive and frequently turn out to be unnecessary (diagnostic) (e.g., in approximately ⅓ of the procedures in patients with multi-vessel disease).
CT can be used to visualize localized narrowing of vessels, such as coronary arteries, cerebral arteries, or other vessels or arteries. The decision of whether or how to clinically intervene is often based on the assessed extent of the narrowing, such as the percentage reduction in the cross-sectional area compared with neighboring portions of the vessel. Some studies have shown that pressure measurements about the stenosis adds additional information beyond the percentage occlusion and can be used to estimate the functional impact of the stenosis and further differentiate the patient's treatment to improve the patient outcome over the treatment that would have been performed on the basis of the percentage occlusion alone.
Therefore, it would be desirable to design a system and method for estimating vascular flow that overcome the aforementioned drawbacks.